Which equation is the inverse of y = 9x^2 - 4?

First swap the x and y variable, then isolate y.

y = 9x^2 - 4
x = 9y^2 - 4
x + 4 = 9y^2
(x+4)/9 = y^2

plus or minus
[tex] \sqrt{((x + 4) \div 9} = y[/tex]